Recently, electronic cameras which record the image of an object using a solid-state image pick-up device, such as a CCD (charge-coupled device) array instead of a silver salt film have been popularized. Generally, there are still cameras for picking up still images and video cameras for picking up dynamic images. Electronic cameras have a solid-state image pick-up device with many detecting elements, each corresponding to an image element, and these are arrayed two-dimensionally along a plane that is perpendicular to the optical axis of the optical system of the electronic camera.
In such electronic cameras, light is incident substantially normally onto the detecting elements that are positioned at the central part of the array surface. However, such cameras have had a problem of low light-detecting efficiency for light that is incident at the periphery of the array surface. The low light-detecting efficiency arises because the light at the periphery of the array surface is incident obliquely onto the detecting elements. Moreover, in many cases, the light-intercepting surface and the image plane of the detection elements arranged at the periphery of the array surface are not coincidental due to curvature of field of the optical system. Thus, another problem was that the image was out of focus at the periphery of the array surface. These problems have been solved previously by imposing strict restrictions on the design of the optical system for electronic cameras.
However, in response to recent demands for miniaturization of electronic still cameras, it is desirable to reduce restrictions, as far as possible, in the design of the optical system of electronic cameras. Therefore, it has been desired to improve the light-intercepting efficiency of the detecting elements of an electronic image pick-up device without imposing restrictions on the design of the optical system of electronic cameras.